实体框架5无法更改该关系，因为一个或多个外键属性不可为空

Question

I receive the fore mentioned error when trying to delete an entity.

This entity has a foreign key to a list table, but I can delete the DB entry without a problem from Heidi MySql client.

I'm trying to clear the child entities, but when i call SaveChanges on the context, it throws the mentioned error.

nquote_orderheaders header = portalDb.nquote_orderheaders.Single(f => f.QuoteOrderNumber == id);

        header.nquote_orderlines.Clear();
        portalDb.SaveChanges();
        portalDb.nquote_orderheaders.Remove(header);
        portalDb.SaveChanges();

Answer 1

Using .Clear() on a navigation property doesn't remove them from the database, it only clears your collection in your code. You need to iterate over your orderlines to remove them one by one.

Another possibility is to enable cascading delete feature, which allows child entities removal if parent entity is removed.